Isobutene and/or isoamylenes from cat poly gasoline

ABSTRACT

The conversion of cat poly gasoline to isobutene using an olefin disproportionation reaction is increased by subjecting a heavier olefin fraction separated from the olefin disproportionation effluent to a high temperature treatment with MgO prior to recycle of said fraction to the olefin disproportionation reactor. In a preferred embodiment, isoamylenes are advantageously prepared using a second olefin disproportionation step which employs the isobutene-containing stream as the feedstock.

United States Patent Reusser 151 3,696,165 i4 1 Oct. 3, 1972 [54]ISOBUTENE AND/OR ISOAMYLENES 3,590,094 6/1971 Reusser et a]. ..260/683FROM CAT POLY GASOLINE Primary Examiner-Delvert E. Gantz [72] Inventor.giggled E. Reusser, Bartlesville, Assistant Examiner- C E SpresserAttorney-Young and Quigg [73] Assignee: Phillips Petroleum Company [22]Filed: June 1, 1970 $1 f 1 b e conversion 0 cat p0 y gaso me to isoutene using [21] Appl' 42,092 an olefin disproportionation reaction isincreased by T subjecting a heavier olefin fraction separated from the52 us. Cl. ..260/683 1), 260/6832 Olefin effluem a high tempera- [51]Int. Cl ..C07c 3/62 treatment with Mgo Prior to recycle of Said frac[58] Field of searh 260/683 D 6832 tion to the olefin disproportionationreactor. In a preferred embodiment, isoamylenes are advantageouslyprepared using a second olefin dispro [56] References Cited portionationstep which employs the isobutene-con- UNITED STATES PATENTS tainingstream as the feedstock.

3,565,969 2/ 1971 l-lutto et al ..260/683 8 Claims, 2 Drawing Figures 3WTHYLENE cAs, 7 2 J I 4 I 1 g lSOBUF-ENES I? 3 6- v 3 5f Z A (L Ll-l O(I) I0 9 Q seg n 2' 3 S F 0 U) U5 5 2 (OIL ISOBUTENE AND/ OR ISOAMYLENESFROM-CAT POLY GASOLINE BACKGROUND OF THEINVENTION l Field of theInvention This invention relates to the preparation of isobutene Thereaction of olefinic materials to produce other olefinic materialswherein the reaction canbe visualized as the breaking of two existingdouble bonds between first and second carbon atoms, and between thirdand fourth carbon atoms, respectively, and the formation of two newdouble bonds, such as between the first and third carbon atoms and thesecond and fourth carbon atoms, respectively, and wherein the two newdouble bonds can be on the same or different molecules, has been calledthe olefin reaction. The breaking and formation of these bonds can bevisualized by using a mechanistic scheme involving a cyclobutaneintermediate. Thus, two-unsaturated pairs of carbon atoms combine toform a four-center (cyclobutane) intermediate which then dissociates bybreaking either set of opposing bonds. This reaction can be illustratedby the following formulas:

Other terms have been utilized to describe the reactions of olefinicmaterials which are within the scope of the olefin reaction as definedabove. These include such terms as olefin disproportionation, olefinported :which effect 'this reaction, including the catalysts of U.S.Pat. No. 3,261,879,Banks, (1966),

and U.S. Pat. No. 3,365,513, Heckelsberg 1968)..

Included among the reactions which fall within the scope of the termolefin disporportionation, there is a reaction which employs ethylene asone of the reactants. That is, the ethylene can be one of theunsaturated pairs of carbon atoms which combines to form the four-center(cyclobutane) intermediate with another unsaturated pair of carbon atomson a different and larger olefinic molecule. For example, ethylene andpentene-2 in the presence of an olefin disproportionation catalyst reactto form butene-l and propylene. Because of the fact that the largermolecule (pentene-2) has been broken to .form the shorter molecules(butene-l and propylene), this specific type of olefindisproportionation reaction has been called ethylene cleavage. Anotherterm which has been applied to this type of olefin reaction isetheneolysis.

Isobutene and/or isoamylene are valuable intermediates in thepreparation of rubbery polymers, e.g., polyisobutene and polyisoprene.Accordingly, the industry desires efficient methods of producing thesematerials using available feedstocks. One available feedstock is amixture of predominantly branched olefins having at least six carbonatomsper molecule. This feedstock has been called cat poly gasoline."Suitable methods are available for its direct preparation. For example,vbutenes and propylene can be cooligomerized in the presence of asuitable oligomerization catalyst to provide such a feedstock. Thiscatpoly gasoline can be cleaved with ethylene in anolefindisproportionation reaction to yield substantial amounts of isobutene.

OBJECTS OF THE INVENTION It is an object of this invention to prepareisobutene. It is a further object of this invention to prepareisoamylenes. Other objects and advantages of the invention will beapparent from a reading of the following disclosure and the appendedclaims.

SUMMARY OF THE INVENTION We have discovered a method whereby isobutenecan be prepared from cat poly gasoline by subjecting the cat polygasoline feedstock to cleavage in the presence of an olefindisproportionation catalyst. The cleaving olefin may be ethylene and/orpropylene. The effluent from the cleavage reaction is subjected to aseparation step in order to provide a stream of C olefins containing asubstantial amount of isobutene and a stream comprising hydrocarbonswhich are heavier than isobutene which is recycled to the cleavage step.Unexpectedly, we have found that the conversion of the cat poly gasolineto isobutene can be increased if the heavier olefin fraction is recycledto the cleavage reactor after contact with a magnesium oxide catalyst ata suitable high temperature followed by deoiling of the contacted streamin a distillation column.

Further, in accordance with the invention, we have discovered thatisoamylenes can be prepared in high conversions by subjecting the Colefin stream containing isobutene and butene-2 to a second olefindisproportionation step. The olefin disproportionation reaction of theC, olefinstream is accomplished in the absence of a cleaving olefin andproduces isoamylenes. The effluent from the second disproportionationstep is then passed to a separation zone wherein isoamylenes arerecovered as product, and an olefin stream comprising materials heavierthan the isoamylenes is recycled to the cleavage unit of the first step.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l of the drawing is a schematicflow diagram of the process of the invention illustrating thepreparation of. isobutene from cat poly gasoline.

FIG. 2 of the drawing is a schematic flow diagram of the process of theinvention illustrating the preparation of isoamylenes from cat polygasoline.

I DETAILED DESCRIPTION OF THE INVENTION The significant advantage oftheinvention isthat the ultimate conversion of the cat poly gasoline to thedesired product (isobutene and/or isoamylenes), is substantiallyincreased by contacting the heavier olefin fraction from the separationzone with magnesium oxide of relatively high temperature and thendeoiling the treated material. Although it is not completely understoodwhy the conversion is thus increased, it is believed that when olefinfeedstreams containing a broad variety of olefin materials are subjectedto ethylene cleavage, ultimate conversion is retarded due to thepresence of certain highly branched structures within the olefinicmaterials. These highly branched olefinic materials are believed to beresistant to the ethylene cleavage reaction. In addition, it is believedpossible that certain materials are generated within the process whichact as poisons on the disproportionation catalyst. In any event, thepassage of the recycle stream containing the resistant branched heavierolefin materials or the materials generated within the process through ahot zone containing MgO followed by deoiling, renders the recycle streammore susceptible to the cleavage reaction, thus increasing theconversion of cat poly gasoline to isobutene and/or isoamylenes.

The invention can best be understood by reference to the drawings. InFIG. 1, cat poly gasoline in line 2 is blended with suitable quantitiesof ethylene (and/or propylene) from line 3, and introduced via line 4into olefin disproportionation (DPN) zone 66. The cleavage reactionwithin zone 66 provides an effluent comprising ethylene, propylene,n-butenes, isobutenes, and some amylenes, as well as incompletelyconverted feed materials. The effluent from zone 66 is conducted vialine 6 to separation zone 67 wherein ethylene and propylene areseparated and recycled via line 7 to the ethylene cleavage zone 66. Theisobutene and buteneolefin fraction is separated and recovered via line8. Any undesirable heavy materials can be removed by way of line 10.

A C olefin fraction from separation zone 67 comprising unconverted catpoly gasoline is removed via line 9 and passed into zone 68 andcontacted with catalytic MgO at elevated temperatures. Subsequent totreatment in zone 68, the C olefin fraction is withdrawn via line 11 andpassed to distillation zone 69. Within distillation zone 69, the Colefin fraction is deoiled, the oil being removed from the system by wayof line 12. The deoiled C effluent passes from zone 69 via line 13 andis returned to stream 2 for recycle via line 4 into the cleavage zone66.

FIG. 2 of the drawing illustrates a process wherein isoamylenes areprepared utilizing the hot MgO treatment described above and anadditional olefin disproportionation unit to convert isobutene andbutenes to isoamylenes. Cat poly gasoline in line 21 is combined withethylene (and optionally propylene) from line 22 in line 23 andsubjected to cleavage within olefin disproportionation (DPN) zone 76.The effluent from zone 76 in line 24 is passed to separation zone 77wherein ethylene and propylene are removed and recycled via line 26 tothe ethylene cleavage unit 76. A C olefin fraction is removed from zone77 via line 28 and subjected to the hot MgO treatment within zone 78.The treated C olefin fraction is removed from zone 78 via line 29 andpassed to distillation zone 79 wherein the MgO treated fraction issubjected to deoiling conditions. Oily products of the MgO treatment areremoved from distillation zone 79 via 31. The deoiled C olefin fractionis removed from zone 79 via 32 and returned to the cleavage unit 76 vialines 32, 21, and 23. Any undesirable heavy materials which are formedwithin unit 76 are removed from separation zone 77 via line 25.

A stream comprising a substantial amount of isobutenes, butenes, andoptionally some propylene, is conducted via lines 27 to olefindisproportionation (DPN) zone 81. Therein, the olefin disproportionationreaction of isobutene and butene-2 produces substantial quantities ofisoamylene. The reaction of isobutene and propylene produces additionalquantities of isoamylenes. The effluent from the reactor 81 is conductedvia line 33 into separation zone 82 wherein propylene and ethylene areseparated and recycled to ethylene cleavage zone 76 by way of lines 37and 26. Unconverted isobutene and normal butenes are returned from zone82 via lines 38 and 27 to reaction zone 81. A C olefin fraction isremoved from the separation area 82 by way of line 34 and returned toethylene cleavage zone 76 via lines 32, 21, and 23. As in separationarea 77, any undesirable heavy materials can be removed from the systemvia line 39.

Product isoamylenes are recovered from zone 82 through line 36. Ifdesired, the C fraction from separation zone 82 can be combined with theC fraction from separation area 77 and treated with the hot MgO in zone78.

Magnesium oxide is known to be a double bond isomerization catalyst,and, as discussed in more detail hereinbelow, it is used in thiscapacity in the present invention process to facilitate the olefincleavage reaction step by being used in conjunction with a solid olefindisproportionation catalyst. Catalytic MgO is not known to haveappreciable skeletal isomerization activity. It has also been found thatwhen liquid materials such as hydrocarbons are percolated through a bedof magnesium oxide, some purification of the hydrocarbon stream isobtained, presumably by adsorption. The purification treatment usingmagnesium oxide is ordinarily carried out at relatively lowtemperatures, such as room temperatures, and can be used in the processof the invention to extend or preserve the life of the olefindisproportionation catalyst against poisons which can be present in thevirgin cat poly gasoline feed.

It was surprising, however, that the processability of the C olefinrecycle streams can be further improved with respect to the olefincleavage reaction by treatment with magnesium oxide at high temperaturesfollowed by deoiling of the stream. It was observed that the effluentfrom a high temperature magnesium oxide treatment was somewhat yellow incolor. The yellow colored material was much less volatile than the bulkof the olefinic material in the treated stream. Thus, it was found thatthe magnesium oxide high temperature treatment coupled with a deoilingtreatment provided a very beneficial effect by increasing the conversionto the desired product olefins when this stream was recycled to theolefin cleavage reaction subsequent to the treatment.

The high temperature magnesium oxide treatment can use any suitablecontacting technique such as fixed bed or fluidized be reactors. Themagnesium oxide can be in any suitable catalytic form ranging from afine powder to prills or tablets. The magnesium oxide which is thepreferred agent for use in the treatment step of the invention is theactivated catalytic material which is known in the art. That is, thematerial has a surface area of at least about lm lg and has beensuitably activated by heat treatment. The magnesium oxide can beobtained from naturally occurring materials, such as the mineralBrucite, or can be synthetically prepared by known methods. Minoramounts of other materials such as silica or alumina can be present, butthe material is principally magnesium oxide. The magnesium oxide isactivated and/or regenerated by heating in flowing air at 8001,400 F forabout 0.1 to about hours. The activation treatment in air can befollowed, if desired, by heating in other gases such as, for example,nitrogen, argon, carbon monoxide, and the like.

The magnesium oxide high temperature treatment of the C olefin recyclestream is carried out at a temperature in the range of from about 500 toabout 900 F, at any suitable pressure in the range of from about 0 toabout 2,000 psig, and at a weight hourly space velocity in the range offrom about 1 to about 100, preferably 3-20 WHSV. In the deoiling stepwhich follows the magnesium oxide treatment, the treated material isdistilled in any suitable way such that the lighter, more reactiveolefins are separated from the relatively nonvolatile undesirablematerials. Ordinarily, about 80 to about 95 percent, preferably about 90to 95 percent, of the treated material is carried overhead, theremainder being left behind in the bottoms and discarded.

Any catalyst having activity for converting olefins in accordance withthe above-described olefin disproportionation reaction can be employedfor the olefin disproportionation steps of the invention. Thesecatalysts include both heterogeneous catalysts which are capable ofolefin disproportionation activity in the presence or absence of aliquid hydrocarbon solvent and homogeneous catalysts which require thepresence of a hydrocarbon diluent during the reaction. Of course, wherethe feed olefin is liquid under normal reaction conditions, it canfunction as a diluent for the homogeneous catalyst. For the olefindisproportionation steps of this invention, particularly for the firstdisproportionation step, the heterogeneous catalysts are preferred.

The heterogeneous catalysts which are particularly suitable for theprocess of the invention include tungsten oxide on silica, tungstenoxide on alumina, molybdenum oxide on alumina, rhenium oxide on alumina,rhenium oxide on aluminum phosphate, molybdenum oxide on aluminumphosphate, and molybdenum hexacarbonyl on alumina. These catalysts arethe subject of U.S. Pat. No. 3,261,879 (Banks) of July 19, 19 66; U.S.Pat. No. 3,365,513 (Heckelsberg) of Jan. 23, 1968; British Pat. No.1,054,864 (British Petroleum) of Jan. 11, 1967; U.S. Pat. No. 3,463,827(Banks) of Aug. 26, 1969; and U.S. application Ser. No. 846,977, filedAug. 1, 1969, now abandoned.

The preparation, activation, and maintenance of the heterogeneous olefindisproportionation catalysts are known in the art, and with reference tothe specific systems as discussed above, are disclosed in theabovementioned patents and applications. The various solid catalystsexhibit different optimum reaction temperatures, pressures, and contacttimes for the olefin disproportionation reaction. Accordingly, thespecific reaction temperature, pressure, and contact time for thedisproportionation reaction employed in the process of the invention iseasily within the skill of one in the art.

Any of the above-mentioned heterogeneous catalysts, when employed in theolefin cleavage reaction step of the invention, preferably employs asuitable double bond isomerization catalyst such as magnesium oxide incombination with the olefin disproportionation catalyst. The magnesiumoxide can be suitably comingled with the solid olefin disproportionationcatalyst and employed in a single olefin cleavage reactor. The magnesiumoxide in combination with the olefin disproportionation catalystfunctions as a double bond isomerization catalyst within the olefinreaction zone and facilitates the olefin cleavage step. Other suitablecombination catalysts are disclosed in copending applications Ser. No.627,635, Banks, filed Apr. 3, 1967,

' now abandoned, Ser. No. 678,499, filed Oct. 27, 1967,

now abandoned, and Ser. No. 678,489, filed Oct. 27, 1967.

Before contact with the disproportionation catalyst in the firstcatalytic zone, the cat poly gasoline is blended with ethylene and/orpropylene in proportions which can range from about 1 to about 20,preferably from 4 to about 10 mols of ethylene and/or propylene per molof feed olefin.

The catalysts employed in the second olefin disproportionation step ofthe invention, i.e., the disproportionation of the C olefin-containingstream, can be any of the above-mentioned catalysts. Although magnesiumoxide can be used in conjunction with the solid olefindisproportionation catalyst, it is presently preferred not to use theMgO combination catalyst in this step of the invention.

The separation steps have been simplified in the FIGURES of the drawingand can, in actual operation, represent a number of consecutiveseparation means such as fractionation and distillation columns and thelike. Any convenient sequence of separation steps can be used. For thesake of brevity, the drawings have excluded such apparatus as pumps,heat exchangers, valves, and the like.

Except for the quantity of high boiling material discarded from the hightemperature magnesium oxide treatment, there are no significantby-products from the process.

Paraffinic materials which may be formed in the process of theinvention, can be removed at any convenient point in the processtogether with any paraffins which may have been present in thefeedstock. In addition, it has been found to be generally advantageousto deoil the feed prior to entering any catalytic stage of the process.This is done to minimize the accumulation and carry-over of smallamounts of materials which might poison or otherwise shorten the life ofthe catalyst. Accordingly, the process may contain other deoiling unitsin addition to the one following the magnesium oxide high temperaturepurification unit.

The invention is illustrated by the following examples, which are forthe purpose of illustration only, and should not be construed aslimiting the scope of spirit of the invention as described hereinabove.

EXAMPLE I A C recycle olefin stream obtained from the ethylene cleavageof cat poly gas (a C olefin stream obtained by the catalyticco-oligomerization of propylene and butenes) was treated according tothe process of the invention to render it more reactive on furtherpassage through the catalytic cleavage zone.

TABLE] Control lnvention On Stream Time hrs. 1 16-2 Uril 3 4V:Conversion,%(1) 40 35 51 45 43 A MgO-containing bed was prepared bycharging 25 5 g of a 20 65 mesh catalytic grade magnesia in a tu-(UConversion of 1+ Olefins C5 and lighlerolefinsbular steel reactor andactivating it at 1 ,000 F in flowing air for 1 hour. It was thencontacted in flowing CO The data in the above table show that treatmentof for minutes and then cooled to 750 F. under CO. the recycle streamaccording to the process of the in- The above C recycle olefin streamwas first perco- 10 vention results in greater conversion and theincrease lated through an adsorption bed of MgO/SiO at room inconversion persists throughout the cycle of catalyst temperature andthen passed through the MgO bed at life. 750 F, at atmospheric pressure,and at a weight The following illustrative examples are presented forhourly space velocity of about 5. l 5 the purpose of illustrating theoverall process of the in- About 2 liters f the yellowcolored effluentwere vention. 1n the absence of actual plant runs, the matericollectedand distilled to an overhead temperature of balances presented b l beencalculated to 145 C and a pot temperature of 167 C, at atmospheric Showthe 9 of the mvemlon pressure. About 90 percent of the effluent wastaken overhead, while the yellow color was essentially left be-ILLUSTRATIVE EXAMPLE 1 hind. The effluent was distilled because itsellow color Cat poly gas is converted to isobutene and butenes in couldnot readily be removed by percolation through the customar adsor tionbed f M O/ l accordance with the process as deplcted in FIG. 1. Silica61 y p s 0 g mo or Olefin cleavage unit 66 employs a tungsten oxide onsil- Th g I l f th b t t d l f ica olefin disproportionation catalyst incombination e e y ene Savage 0700 F $138 6 0 2 with magnesium oxide. Theweight ratio is 5:1 magnesimlxture was Carrie P at um oxide to tungstenoxide on silica. The reaction tem- WHSV at an f defin ran) of by fperature is 700 F, the pressure is 400 psig, and the the materialthrough a mixed catalyst bed comprising weight hourly space velocity isThe ratio of g of 20360 mesh WOK/ S102 Olefin dlspropomona' 30 ethyleneto feed olefins in the cat poly gas in zone 66 is catalyst g 2O+60 meshMgo double maintained at 4:1 on a molar basis. The high temperabondisomerizatlon catalyst. Another bed containing ture one employs as thecatalyst and the tem. 3.5 g of the MgO imm i ly pr the mlXed perature inthat zone is 750 F, the pressure is ambient, The catalytic beds wereactivated by heating at 1,000 and the weight hourly space velocity is 5.The composi- Fin flowing air for 3 hours,followed by flowing CO for tionof the various streams of the process are sum- 15 minutes, and thencooled to the 700 F operating marized below in Table 11 in terms ofweight parts per temperature. The feed was percolated at room temhour.

TABLE 11 wt. parts/hr Stream 2 3 4 6 7 8 9 1 1 12 13 Cat Poly Gas 27.6527.65 Ethylene 8.47 36.40 27.93 27.93 Propylene 13.60 13.63 13.60lsobutane 0.06 0.06 n-Butane 0.06 0.06 Butene-l 3.08 3.08 lsobutene18.58 18.58 c-Butene-2 5.06 c-Butene-Z 5.06 5.06 lsopentane 0.06 0.060.06 0.06 0.06 3-Methylbutene-l 1.26 1.26 1.26 1.26 1.26 n-Pentane &Butadiene 0.15 0.15 0.15 0.15 0.15 Pentene-l 0.07 0.07 0.07 0.07 0.07Z-MethyIbutene-l 1.17 1.17 1.17 1.17 1.17 t-Pentene-Z 2.21 2.21 2.212.21 2.21 c-Pentene-Z 2-Methylbutene-2 2.85 2.85 2.85 2.85 2.85 C5+Olefins 14.58 16.93 16.93 16.93 2.35 14.58

Total 27.65 8.57 100 100 41.53 33.74 24.70 24.70 2.35 22.35

perature through an adsorption bed of MgO/mole sieve M before beingpassed into the reaction zone.

The process as depicted in FIG. I of the drawing pro- -vides 18.58 wt.parts per hour of isobutene and 15.04

For purposes of comparison, another portion of the .wt. parts per hourof butenes, based on a charge rate of The effluents from these twocleavage runs were collected and/or sampled at selected intervals andanalyzed. The results are shown in the following Table l.

27.65 parts per hour cat poly gasoline and 8.47 wt. parts per hour ofethylene.

ILLUSTRATIVE EXAMPLE I1 lsoamylenes are prepared using a process of theinvention as is depicted in FIG. 2 of the drawing. Olefin cleavagereactor 76 employs a tungsten oxide on silica olefin disproportionationcatalyst in combination with magnesium oxide which is identical to thatemployed in Illustrative Example 1 above, in reactor 66. The hightemperature magnesium oxide zone 78 employs the same catalyst and thesame conditions as zone 68 in 11- lustrative Example I with theexception that the temperature is 775 F. Olefin disproportionation zone81 employs a tungsten oxide on silica catalyst and operates at atemperature of 842 F, a pressure of 300 psig, and a weight hourly spacevelocity of 100. The composition of the various stream of the processare summarized in Table 111 below in terms of weight parts per hour.

TABLE III wt.parts/hr stre- No. Cat Poly Gas 15.76 15.76 Ethylene 13.5133.54 15.93 15.93 Propylene 16.93 17.63 17.63 Butene-l 3.08 3.08isobutene 22.58 22.58 t-Butene-2 7.02 7.02 c-Butene-2 5.06 5.06lsopentane 0.06 0.06 0.06 0.06 3-Methylbutene-l 3.26 3.26 3.26 3.26n-Pentane &Butadiene 0.15 0.15 0.15 0.15 Pentene-l 0.07 0.07 0.07 0.072-Methyl butene-l 3.17 3.17 3.17 3.17 t-Pentene-Z 2.21 2.21 2.21 2.21c-Pentene-2 nil nil nil nil Z-Methylbutene-Z 2.85 2.85 2.85 2.85 C-i-olefins 22.00 16.93 15.83 14.58 Heavies 1.10 1.25 total 20.28 15.07100 100 1.10 15.93 55.37 27.60 27.60

Stream No. 31 32 33 34 36 37 38 39 Cat Poly Gas Ethylene 4.10 4.10Propylene 16.93 16.93 Butene-l 1.69 1.69 lsobutene 12.42 12.42t-Butene-Z 3.86 3.86 c-Butene-2 2.78 2.78 lsopentane 0.06 3-Methy1-Butene-l 3.26 3.85 3.85 n-pentane& Butadiene 0.15 Pentene-l 0.07Z-Methylbutene-l 3.17 7.32 7.32 t-Pentene-Z 2.21 0.70 0.70 c-Pentene-2nil 0.30 0.30 2-methy1- butane-2 2.85 12.25 12.25 C olefins 22.00 7.427.42 Heavies 1.25 2.50 2.50

'Total 1.25 33.77 76.12 7.42 24.42 21.03 20.75 2.50

The above table illustrates that 3.85 weight parts per hour3-methylbutene-l, 7.32 wt. parts per hour of 2- methylbutene-l, and12.25 wt. parts per hgur o f 2 methylbutene-Zare produced based on acharge of 15.76 wt. parts per hour of cat poly gasoline and 13.51 wt.parts per hour of ethylene.

Reasonable modification and variation in the invention as describedherein is possible without departing from the spirit and scope thereof.

lclaim:

1. In a process for the preparation of isobutene which comprisescontacting in a first reaction zone cat poly gasoline and ethylene orpropylene in the presence of an olefin disproportionation catalystsuitable to cause the olefin cleavage of the cat poly gasoline toproduce a stream comprising said isobutene and a stream comprisingolefin hydrocarbons heavier than isobutene, the improvement comprisingcontacting the stream comprising olefin hydrocarbons heavier thanisobutene with magnesium oxide at a temperature in the range of fromabout 500 to about 900 F and subsequently deoiling the magnesiumoxide-treated stream, and returning the treated stream to said firstreaction zone.

2. The process of claim 1 wherein the contact of the stream comprisingolefin hydrocarbons heavier than isobutene with magnesium oxide isaccomplished at a pressure of from about 0 to about 2,000 psig, at aweight hourly space velocity of from about 1 to about 100.

3. The process of claim 2 wherein the deoiling of the magnesiumoxide-treated stream is accomplished in a distillation zone wherein fromabout to about percent of the treated stream is taken overhead andreturned to the first reaction zone.

4. The process of claim 3 wherein the magnesium oxide is activated priorto contact with the heavier olefin stream by heating in flowing air to atemperature of from about 800 to about l,400 F for a period of fromabout 0.1 to about 20 hours.

5. The process of claim 1 wherein the stream comprising isobutenecontains ethylene and butene-Z, said ethg'lene is seg arated from thestream comprising utene, and e resulting ethylene deficient stream 15contacted in a second reaction zone with an olefin disproportionationcatalyst to produce a stream comprising isoamylenes and a streamcomprising olefinic hydrocarbons heavier than isoamylenes, the latterstream being returned to the first reaction zone.

6. The process of claim 5 wherein the stream comprising olefinichydrocarbons heavier than isoamylenes is contacted with hot magnesiumoxide prior to returning the stream to the first reaction zone.

7. The process of claim 6 wherein the stream comprising olefinichydrocarbons heavier than isoamylenes is admixed with the streamcomprising olefinic hydrocarbons heavier than isobutene prior to thelatter stream being contacted with the hot magnesium oxide.

2. The process of claim 1 wherein the contact of the stream comprisingolefin hydrocarbons heavier than isobutene with magnesium oxide isaccomplished at a pressure of from about 0 to about 2,000 psig, at aweight hourly space velocity of from about 1 to about
 100. 3. Theprocess of claim 2 wherein the deoiling of the magnesium oxide-treatedstream is accomplished in a distillation zone wherein from about 80 toabout 95 percent of the treated stream is taken overhead and returned tothe first reaction zone.
 4. The process of claim 3 wherein the magnesiumoxide is activated prior to contact with the heavier olefin stream byheating in flowing air to a temperature of from about 800* to about1,400* F for a period of from about 0.1 to about 20 hours.
 5. Theprocess of claim 1 wherein the stream comprising isobutene containsethylene and butene-2, said ethylene is separated from the streamcomprising isobutene, and the resulting ethylene deficient stream iscontacted in a second reaction zone with an olefin disproportionationcatalyst to produce a stream comprising isoamylenes and a streamcomprising olefinic hydrocarbons heavier than isoamylenes, the latterstream being returned to the first reaction zone.
 6. The process ofclaim 5 wherein the stream comprising olefinic hydrocarbons heavier thanisoamylenes is contacted with hot magnesium oxide prior to returning thestream to the first reaction zone.
 7. The process of claim 6 wherein thestream comprising olefinic hydrocarbons heavieR than isoamylenes isadmixed with the stream comprising olefinic hydrocarbons heavier thanisobutene prior to the latter stream being contacted with the hotmagnesium oxide.
 8. The process of claim 7 wherein said ethylene isreturned to the first reaction zone, and the stream comprisingisoamylenes also contains isobutene, butenes, and propylene, and theisobutenes, butenes, and propylene are separated from the isoamylenesand returned to the second reaction zone.